Two major methods of eye cornea reshaping, are in current use, for correction of abnormal vision, resulting from improper eye focussing (generally, the conditions of myopia, with the perceived image optimal focussing in front of the retina; hypermetropia (hyperopia), with the image optimal focussing beyond the retina; and astigmatism which combines symptoms of both myopia and hyperopia, on a localized basis) The first method, radial keratotomy, involves the surgical incision of the cornea of the eye with deep medial cuts which cause a predictable flattening of the cornea of the eye when the eye heals. The reshaped cornea of the eye, with changed curvature and concomitant changed refraction, causes light or optical rays associated with an image (the perceived image), passing through the lens of the eye, to be refocussed on the retina, with refractive compensation, such as for eye shape deviations from normal. This method is however a major surgical one, and requires considerable skill in proper utilization. Improper incisions can detrimentally permanently affect the eye, without recourse to ready correction. Scarring is not uncommon and some deaths have resulted. In addition, the correction may also vary with time.
The second major method for vision correction involves the use of the excimer laser which is on the verge of FDA approval for widespread use. The excimer laser operates by controllably ablating away portions of corneal tissue, mostly through photochemical disintegration of the tissue, to either increase or decrease the effective curvature of the front of the cornea (i.e. corneal tissue), thereby correctively refocussing images on the retina. While this procedure is less invasive and traumatic than the radial keratotomy, and has had no associated injuries in over 250,000 procedures, it is nevertheless accompanied by some heat generation and dehydration, for an extended period of time. The ablation technique leaves the surface structured on a microscopic scale, and also affects adjacent corneal surface tissue and, with the plumes, results in an inaccuracy of correction of up to one diopter or more deviation from the desired value. This compares unfavorably with corrective lenses and contact lenses which provide a more accurate correction to within 0.25 diopters deviation. In addition, some haze usually results from wound healing effects.